Remove Paint brush through python
The brushes collection is available thru bpy.data.brushes  Like most (maybe all) ID object collections in blender, items can be removed with collection.remove(obj).

import bpy
# get the brush
brush = bpy.data.brushes.get("Brush67")

# if brush is None well make a new one for example

if brush is None:
    brush = bpy.data.brushes.new("Brush67")

# remove the brush

bpy.data.brushes.remove(brush)